1. Field of the Invention
The present invention relates to a spread spectrum communication system for wireless communications, such as mobile communications and wireless LAN systems. Particularly, the present invention relates to a spread spectrum communications system for high-speed communications.
2. Related Art
To achieve higher communication speed using spread spectrum techniques, an M-ary method, a parallel method, and a parallel combination method have been proposed. (See AKECHIKA, Yasuaki, et al., Electronic Information Communication Society Papers, B-II, Vol. J74-B-II, No. 5, pp 207-214, May 1991.) In the M-ary method, a plurality of PN codes are initially prepared. Each PN code corresponds to predetermined bit patterns of a transmitting signal. One PN code is selected and transmitted based on which signal is being transmitted.
In the parallel method, a plurality of PN codes are initially prepared. The data to be transmitted is divided into parallel signals, spread by respective PN codes and transmitted in parallel. The parallel combination method also utilizes a plurality of PN codes. A combination of PN codes is selected based on which of the signals are to be transmitted, and one or a plurality of PN codes are transmitted in parallel.
In such high speed spread spectrum communication methods, the receiver must be able to receive a plurality of PN code sequences simultaneously. Thus, the demodulator needs a plurality of matched filters. Faster speed is desired for a circuit scale. In conventional high speed communication methods, many PN codes must be assigned to one user, even though the number of available PN codes is limited. Therefore, the number of users was limited.